Add an option to disable qr codes

src/qr_code.h

@@ -23,6 +23,8 @@
 #ifndef QR_CODE
 #define QR_CODE
 
+#ifdef QRCODE
+
 #define QRCODE_FILENAME_EXT ".QRcode"
 
 /* Converts a tox ID string into a QRcode and prints it into the given filename.
@@ -42,4 +44,6 @@ int ID_to_QRcode_txt(const char *tox_id, const char *outfile);
 int ID_to_QRcode_png(const char *tox_id, const char *outfile);
 #endif /* QRPNG */
 
+#endif /* QRCODE */
+
 #endif /* QR_CODE */